The present invention relates to multi-antenna wireless systems in general, and, more particularly, to techniques for modeling capacity of propagation and reception of multi-antenna wireless signals in multi-path environments.
Designing workable antennas and antenna arrays, although a non-trivial task, is not sufficient to optimize the performance of information transfer between a transmitter and a receiver. The antenna arrays need to be optimized in design, location, and operation, taking into account the surrounding environment. Objects in the environment in which an antenna array operates often reflect and diffuse a transmitted signal along the way to a receiving antenna, thereby influencing its efficiency.
FIG. 1 depicts an illustrative terrestrial environment that comprises: transmitting antenna 101, receiving antenna 102, forest 111, building 112, building 113 and boat 114. As a signal is transmitted from transmitting antenna 101 to receiving antenna 102, the signal is likely to be scattered by objects in the environment that are near and between the transmitting antenna and the receiving antenna. A good antenna design considers the scattering of the transmitted signal.
In the prior art, the multi-path character of the environment has not, in general, been considered in designing antennas. Rather, designers have usually made the simplifying assumption that the antennas operate in xe2x80x9cfree space.xe2x80x9d This meant that to design a good antenna array one had to place antennas in the array so that they can transmit to or receive from one particular direction, the so-called line of sight to the receiving/transmitting array. FIG. 2 depicts transmitting antenna 201 and receiving antenna 202 in free space. When antennas are operating in free space, it is assumed that the transmitted signal radiates without scattering from the transmitting antenna to the receiving antenna. This assumption is perhaps reasonable for rural environments, but is untenable for many urban and outdoors applications (e.g., cities, large structures, buildings, office spaces etc.). The result is that antenna arrays designed and fabricated to operate in free space provide poor performance when operating in multi-path, diffusive environments. Therefore, the need exists for a technique that accounts for the multi-path character of the environment in which the antennas are to operate.
Also, the prior art does not address the need for optimizing transmitter configurations within diffusive and reflecting environments, such as a building, when both power and diversity are factors in such an environment. This results in prior art systems that are designed to transmit more power than necessary for a given configuration and systems that could have larger information capacity if changes were made to the locations and number of antennas in the environment. The prior art does not address the information capacity of a system independent from the power of the signal. Therefore, a need exists for a technique that accounts for transmitted power and diversity of the transmitted and received signals in order to achieve a desired information capacity, especially in systems with multiple-input-multiple-output (MIMO) configurations.
The present invention makes advantageous use of the statistical properties of a function, S(r, k, xcex5; rxe2x80x2, kxe2x80x2, xcex5xe2x80x2) of the propagation and reception of wireless signals in order to provide a method for modeling an information capacity of a multi-antenna wireless system, especially in a diffusive environment where previous methods result in systems that have lower information capacities, or higher power use for equivalent information capacities.
Some embodiments of the present invention provide an ability to design, install and operate antennas without some costs and disadvantages of techniques in the prior art. In particular, the illustrative embodiment of the present invention not only considers the multi-path character of the environment in which the antennas will operate, but also takes advantage of the multi-path character of signals caused by reflection and scattering. Furthermore, the illustrative embodiment of the present invention can provide the design which when installed and operated provides optimal channel information capacity by taking advantage of the multi-path character of the environment in which the antennas operate.
The illustrative embodiment of the present invention models the multi-path character of the environment using a diffusive or statistical model and uses an iterative approach to predict the performance of candidate antenna designs in that environment and to suggest improvements in the design until the predicted performance reaches an optimal or otherwise acceptable level.
In another aspect, the invention provides a method for configuring a wireless communication system that has a plurality of antennas. The method includes solving one of a diffusion equation, a Boltzmann equation, and a ray tracing equation to evaluate an average of some function of a two-point complex amplitude transmission matrix representative of the communication system; and calculating a set of quantities from the evaluated complex amplitude transmission matrix, each of the quantities representative of the performance of a communication link or communication system.
In other embodiments, methods described herein are performed on computers or application specific processors. In these embodiments, a program storage medium encodes a computer executable program of instructions for performing the various steps of one of the above methods. Exemplary computer storage media for such programs include: magnetic tapes, magnetic disks, compact optical disks, hard drives, read-only-memories, and active memory devices.